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Fundamental and applied studies on cyanide formation in the carbon liner of an industrial aluminium electrolytic cell


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Yap, Bin Kiat 1985 , 'Fundamental and applied studies on cyanide formation in the carbon liner of an industrial aluminium electrolytic cell', Research Master thesis, University of Tasmania.

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The objective of this study was to investigate the presence
of cyanide in the industrial aluminium electrolytic cell.
Therefore, it was an aim of this investigation to identify
the favoured regions of cyanide formation in potlining, and
conduct parallel laboratory studies to determine some of the
chemical factors likely to influence cyanide formation.
The study was conducted in three stages. The first stage
involved autopsies of cells of various ages, design and
construction in detail. This was followed by extensive
sampling of sections of the trenched sidewalls and cathode
combined with chemical analyses of the specimens, to enable
mapping of the cyanide distribution profiles. Examination
of these profiles revealed that major amounts of cyanide
were generally concentrated in the carbon sidewall region
near the collector bars and to a lesser extent in the
cathode near the mid-section of the pot. In particular,
carbon that was heavily impregnated with metallic sodium and easily accessible to air ingress, was found to contain high
concentrations of cyanide. Thus, from the cyanide profiles
it: was evident that air ingress through the collector bar
seals of the cathode, and sodium penetration of the carbon
governed the favoured region for cyanide formation during
normal pot operation.
In the second stage, an examination of the kinetics of
sodium cyanide formation in carbon-mix was performed in the
laboratory. Metallic sodium was reacted with carbon and
gaseous nitrogen over a range of temperatures. Rate plots
derived from a combination of thermogravimetric and integral
analysis techniques indicated that there was increasing
reactivity with increase in sodium content during the
initial stages of reaction. Furthermore, rate data obtained
appeared to fit a second-order reaction relative to reactant
sodium after the initial burst of reaction.
Further laboratory investigations were conducted to
establish the temperatures required for cyanide formation,
and determine the susceptibility of different forms of
carbon to cyanide generation. The carbon types ranged from
plant derived carbon-mix through commercial preformed
cathode material to high purity graphite. Whilst cyanide
formation was found to readily occur in the temperature
range of 500-600°C in all the carbons tested, the less
ordered carbon-mix was significantly more vulnerable.
However, highly graphitised carbon was the least susceptible
to cyanide formation within its structure.
Moreover, the reaction was accelerated by the presence of
small amounts of iron impurity. Laboratory tests also
indicated that the predominant cyanide-containing species
formed in potlinings was most likely uncomplexed sodium
The overall results obtained from laboratory studies were
consistent with plant measurements and observations derived
from the complex industrial situation. Conclusions drawn from this work may have implications in terms of future cell
design, and the ultimate impact of spent potlinings on the
surrounding environment.

Item Type: Thesis - Research Master
Authors/Creators:Yap, Bin Kiat
Keywords: Electrolytic cells, Cyanides, Aluminum cell
Copyright Holders: The Author
Copyright Information:

Copyright 1985 the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (M.Sc.)--University of Tasmania, 1986. Bibliography: leaves 83-86

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